1. Field of Invention
The present invention relates to a structure of semiconductor device and a method of fabricating the same. More particularly, the present invention relates to a structure of memory device and a method of fabricating the same.
2. Description of Related Art
The charge-trapping type memory device is a new non-volatile memory, in which for example a silicon nitride charge trapping layer is used to replace with the traditional polysilicon floating gate of the flash memory. Because electrons will be captured by the charge trapping layer, the electrons injected to the charge trapping layer are trapped at a local area in a Gussian distribution, instead of an even distribution. Further, since the electrons are localized only at certain region of the charge trapping layer, sensitivity for tunneling oxide defection is smaller and leakage current is hardly occurred.
Referring to FIG. 1, a partial enlarged view of the cross section of the conventional charge-trapping type flash memory is shown. The flash memory comprises a substrate 100, a charge trapping layer 102, and a gate conductive layer 104, wherein the charge trapping layer 102 comprises a first oxide layer 102a, a nitride layer 102b, and a second oxide layer 102c. In the conventional process of fabricating the flash memory, after a bit-line etching is performed, the substrate surface may be overetched, thus leading to silicon-loss. And the silicon-loss further leads to an excess oxide encroachment as shown in the position E1 in FIG. 1 during poly re-oxidation. The enlarging of the first oxide layer 102a in the edge region obviously reduces the charge efficiency of passing the enlarging first oxide layer 102a into the nitride layer 102b, such that the edge of the nitride layer 102b used to store charges become more difficult for charges to enter the nitride layer 102b to negatively affect the device performance. Particularly, that causes the high degradation in erase efficiency after the device undergoes the endurance cycling test several times and induces the charge retention to become worse.